Archaeologist William Saturno of Boston University excavates the house in the ruins of the ancient Maya city of Xultún. 'Younger Brother Obsidian,' as labeled on the north wall of the Maya city’s house by an unknown hand, was painted in the 9th century A.D., and may have been the town scribe.

Archaeologists exploring Mayan ruins deep in the Guatemalan jungle say they have discovered a tiny workroom where scribes or priests performed calculations tied to the Maya's intricate calendar system.

Some of the numbers and hieroglyphs adorning at least two of the room's walls are related to tracking time using the Maya's lunar calendar, one of at least 13 interlinked calenders the culture maintained, according to a research team announcing the results Thursday.

In addition, time references in one set of symbols appear to extend almost 1,600 years beyond Dec. 21, 2012, a date some doomsayers have claimed is the end of time by Maya reckoning.

The calculations and tables represent the oldest evidence yet showing Maya working and even reworking calculations that underpinned their religious ceremonies or identified the most auspicious periods for completing projects.

The room dates to around 800 AD and also sported a detailed wall painting of the local king, as well as murals depicting other figures, including one who could have been the scribe or artist who painted the royal portrait.

Finding murals of any kind on buildings this old – and as exposed to the destructive elements of a tropical climate and looting as this room had been – is rare enough.

“I was shocked” to see the king's portrait in a niche in one of the walls, says William Saturno, a Boston University archaeologist who led the research team, reporting its results in Friday's issue of the journal Science.

The Maya produced books filled with astronomical and astrological tables that allowed scribes to determine when eclipses would occur as well as when religious events should occur. Perhaps the most complete compilation of these tables and timetables for religious rites is known as the Dresden Codex – vegetable-ink hieroglyphics on pages made from pounded tree bark coated with a thin stucco layer and produced around 1400.

But a combination of destructive climate and the Spanish conquest have left the Dresden Codex, some other book fragments, and astronomical tables and calendars carved in stone monuments as the only evidence of what the scribes or calendar priests produced.

These previous Mayan records were "all after the fact – the end result of vigorous intellectual and record-keeping culture,” says Dr. Martin, who is not part of the research team that made the discovery.

Therefore the opportunity to gain insights into that culture via inscriptions on what might be termed Maya scribes' "white board" in a small office in Xultún, he says, “is a real surprise.”

In its heyday, the ancient city of Xultún, a regional metropolis in the northeastern corner of Guatemala, spanned some 12 square miles and would have housed tens of thousands of people.

Scientists first visited the site and formally identified it as an important Mayan center in 1915. Over the next 93 years, a handful of expeditions would return to map the hard-to-reach site and begin deciphering its story, carved into stone monuments.

In 2010, Dr. Saturno and colleagues visited the site toward the end of a field season spent studying ruins at nearby San Bartolo. As Saturno tells the story, one of his undergraduate students was exploring a trench looters had dug to reach a mound-covered structure. The student, Max Chamberlain, found a wall fragment that had the barest wisp of color on it.

“I thought: OK, there's not a lot there; it's nothing to write home about,” Saturno recalls. But due diligence, backed by the discovery of a well-preserved wall mural at San Bartolo in a location far better protected from the elements, suggested a slim chance of finding something at Xultún.

Digging into the structure and exposing one wall, he uncovered the image of the king, as well as other figures painted on interior walls.

Some of the hieroglyphics and number arrays “are hard for us to decipher; they defy an explanation right now,” says David Stuart, a specialist in Mayan art and writing at the University of Texas at Austin and another member of the research team.

Still, in analyzing the number and hieroglyphs, the researchers found some familiar patterns.

One array of numbers was arranged in 27 columns, each column of numbers headed by a different symbol for the moon. The columns represented a roughly 13-year-long calendar, based on lunar cycles. The hieroglyphs at the top of each column represented the Mayan god serving as the moon's patron for each of the 27 periods.

“This is something we've never really seen before,” Dr. Stuart says.

For people hunkering down in anticipation of Dec. 21, 2012, the find also sounds the latest in a series of all-clears – indications that Mayan scholars say have been present all along to debunk Dec. 21, 2012 as a cataclysmic moment. One array of Xultún hieroglyphs and numbers refers to 17 baktun – 400-year time spans on the Mayan long-lob calendar, known as the long count. That means the scribes were thinking in terms of a 7,000-year time span. Although Dec. 21, 2012, represents the end of a 13th baktun, the Maya clearly didn't see that as the end of time, the researchers say – merely the end of one cycle and the beginning of another. Saturno likens it to an automobile odometer rolling over from 120,000 miles to 130,000 miles.

For Mayan scholar Mark Van Stone, the find underscores the intellectual sophistication of the Maya's culture. They carved out a civilization in a jungle – which required “remarkable persistence” and (at least initially) a sensitivity to their environment.

Like the Chinese and Egyptians, the Maya used large public displays of writing as a symbol of power. And the culture had a system of numbers, including the use of 0, that allowed them to calculate with large numbers in ways contemporary Greek, Roman, and Hebrew numbering systems didn't allow.

This latest find “is a window into the intellectual history” of the Maya, he says.